text: Clostridium difficile. Clostridium difficile, also known as CDF/cdf, or C. diff, is a species of Gram-positive bacteria of the genus Clostridium that causes severe diarrhea and other intestinal disease when competing bacteria in the gut flora have been wiped out by antibiotics.lostridia are anaerobic, spore-forming rods. C. difficile is the most serious cause of antibiotic-associated diarrhea and can lead to pseudomembranous colitis, a severe inflammation of the colon, often resulting from eradication of the normal gut flora by antibiotics.